1. Field of Invention
The present invention relates to oil permeable internal combustion engine gaskets that are resistant to hydrocarbon oil and a method of rendering these oil permeable elastomeric gaskets resistant to hydrocarbon oil, particularly resistant to absorption and bleeding.
2. Description of Art
A variety of more or less elastomeric materials are used to prepare gaskets used as seals between joined parts of an internal combustion engine to prevent leakage of hydrocarbon oils at the point of joining. These permeable elastomeric materials include natural or organic and synthetic rubbers, such as EPDM, SBR, butyl nitrile and neoprene, chlorosulfonated polyethylene, fluorocarbon containing compounds, urethanes and the like. Preferably the elastomeric material is silicone rubbers which have excellent molding and extrusion properties and form gaskets with good physical properties such as enhanced high and low temperature stability, resistance to compression set at elevated temperatures, and good tear and tensile strength. Silicones can also be formulated to provide a gasket having a low durometer. Gaskets prepared from low durometer formulations provide excellent seals in applications where mated surfaces are uneven or irregular. In spite of the many advantages offered by elastomeric silicones as a gasket material, these gaskets when exposed to hot oil in an internal combustion engine tend to absorb some of the oil. As a gasket and mating metal surfaces of an engine cool after use, the oil absorbed by the gasket migrates from the gasket in both the inner and outer directions. The cycling which results from alternate heating and cooling causes the absorbed oil to permeate the cross-sectional thickness of the gasket until it reaches the outer surface of the gasket where it "bleeds" through and appears as small beads or drops on the outer surface of the gasket.
Other attempts have been undertaken in the past to reduce the absorption characteristics of silicone gaskets to hydrocarbon oil.
U.S. Pat. No. 5,380,770 discloses heat cured silicone rubber compositions to which are added a potassium aluminosilicate filler. According to the invention, the filler improves retention of physical properties and resistance to swelling in hot hydrocarbon oils.
U.S. Pat. No. 4,580,794, discloses a method for manufacturing an engine gasket having reduced oil permeability where a silicone varnish is applied to at least the inner surface of the engine gasket.
Neither of the above references discloses the use of organic coatings such as the parylene series as a means of improving the resistance of elastomeric silicone gaskets to absorption and "bleeding".
U.S. Pat. No. 5,075,174, discloses an elastomeric silicone gasket having reduced surface energy and outgassing qualities for use in computers and electronic equipment. The thickness of the parylene coating is disclosed as from 0.1 to 3 microns in thickness.